31 replies to this topic

[WimpyMiniMan]

Hi there - I seem to have a recurring problem with my headlight selector switch, in that the middle pin has a habit of  melting out of the case and moving away from the connector on the inside of the switch rendering it useless, as well as my headlights. I have replaced the switch twice in 4 months which seems a little often even for a badly made switch. Any ideas how to stop it melting / lower the current to the switch. I have thought about a relay, but I'm a bit of a novice with electrics but I am keen to learn and I know the basics.

 

Kind Regards

George

[Anthony30]

Wired by Wilson makes a pre made loom for the headlights. It also meanS you can upgrade your headlights to H4.

Edited by Anthony30, 23 February 2016 - 10:25 PM.

[Daz1968]

I would check the resistance of wiring as if only standard lights the switch should be up to the job, maybe a bad connection somewhere.

[WimpyMiniMan]

I will have a look 

[KernowCooper]

A high resistance would do what you describe or poor quality spring contacts? removing the current from the switch using relays once you've had a chance to check the connections over would resolve the issue

[WimpyMiniMan]

how would you go about making a relay switch for this application? And what am I testing in the wires?

[dklawson]

If you are not familiar with headlight relays, the easiest thing is to buy a relay kit made for the purpose.  Anthony recommended Wired By Wilson who posts on this board.  Look him up and see what he can offer.  There are also kits on eBay.  However, you often get what you pay for so be prepared to spend a bit more than the lowest eBay item and get a better product.

 

Succinctly, the relay kit will take the job of switching high headlamp current off the dashboard switch so it will last indefinitely.  

[Mini Manannán]

the Wired By Wilson option is the one to go for, it's custom made for minis

[MRA]

You have an underlying fault that needs to be fixed first.

 

Otherwise it will recur and could quite easily result in a thermal event, checking resistances from end to end is one way but a much better method is to use a thermal imaging camera or similar to look for hot spots in the wiring, so do not run your engine and only turn on your lights.  They are fairly cheap to.

[midridge2]

All DIY mini mechanics should have a thermal camera in their tool boxes along with Dry ice for bearings, a must.

[phil hill]

All DIY mini mechanics should have a thermal camera in their tool boxes along with Dry ice for bearings, a must.

I believe there is an "App" for the Apple and probably Android phones which is a thermal image camera.

 

Dry Ice - Plumbers freeze spray = same result.

 

Phil.

[Ethel]

I must be missing something, while unintended resistance in wiring is never good, more resistance in the circuit would reduce the load on the switch. It's too little resistance, in a short downstream of the switch or faulty bulbs to look out for.

[dklawson]

Regardless, the use of relays in horn and headlight circuits reduces the job of the switch to carrying a tiny fraction of the current it dealt with using "standard" factory wiring.  

 

There are a couple of basic electrical formulas for power (heat).  Let's take a moment to look at them.

(Sorry, techno-babble to follow).

 

Power (Watts) = Heat = volts x amps.  With the voltage being a more or less constant, you can see that as you reduce the amps in a circuit, the heat generated is reduced.  A relay does that by using the switch to trigger the relay (the switch no longer carries 5 or more amps, it carries about 100 mA (1/50th the current).

 

Power (heat) is also:  Watts = amps x amps x ohms.  Reducing the resistance in a circuit will help reduce heating... but not as quickly or significantly as reducing the amps (which is squared in the formula).  

 

The resistance causing a switch to get hot and melt is INSIDE the switch at its contacts... not in the circuit wiring.  The only way to protect the switch by reducing circuit resistance is to service the contacts inside the switch.. not the wiring in general.  Fitting a relay is immediately easier than opening a switch to service its contacts.  Fitting relays is also generally cheaper than replacing the switch when you take it apart and lose pieces or give up and have to fit a new one anyway.

 

IR camera?  Not in my budget at this time.  With continually dropping prices... maybe someday.

Edited by dklawson, 24 February 2016 - 01:07 PM.

[russo]

I agree with Doug. First check current draw and if within specs, fit a relay kit.

[Carlos W]

Are they standard headlights?

Current draw through the switch is around 15 amps which is a lot.

A relayed headlight set up reduces the current to both the switch and stalk